1. Field
One or more embodiments of the present invention relate to toners for electrophotography, and more particularly, to toners for developing electrostatic latent images.
2. Description of the Related Art
Volatile organic compounds and particulate matter are typically generated in an electrophotographic printing process of a laser printer. It has been reported that particulate matter, such as fine particles (FP) and ultra-fine particles (UFP), is harmful to the human body. Accordingly, there is a need to limit the amount of the particulate matter generated in the printing process of a laser printer. For example, in 2012, the particle emission rate (PER) was newly introduced into Germany's Blue Angel Certification.
The reason for the generation of the particulate matter in the electrophotographic printing process is that heat and pressure are applied to a toner in a toner fusing step. The particulate matter, such as FP and UFP, may be generated from a toner and a fuser roller during the application of heat and pressure to the toner. Stress (heat and pressure) applied to the toner is being further increased according to the demand for high-resolution printing and high-speed printing. Accordingly, the amount of the particulate matter generated from the toner will be further increased.
In order to remove the particulate matter which is generated from the toner, it may be considered that a filter unit is additionally installed at the inside or the outside of the printer. However, the addition of the filter unit may further complicate the structure of the printer. Accordingly, it further makes the maintenance of the printer cumbersome and increases the price of the printer. Eventually, it may seriously reduce a consumer's purchase motivation. Therefore, it is expected that an approach in terms of toner itself may be more efficient in reducing the amount of the particulate matter.
It is preferable that the toner have an excellent fixing property in order to secure reliability of the electrophotographic printing process itself. In particular, for high-speed printing, it is preferable that the toner have a wide fixing (temperature) range. In order for the toner to have a wide fixing temperature range, it is preferable that the toner be effectively fixed even at a lower temperature. This may be expressed as a minimum fusing temperature (MFT). In addition, in order for toner to have a wide fixing range, it is preferable that the toner exhibit an excellent anti-offset property even at a higher temperature. The term “offset” denotes that at least a portion of toner constituting a toner image which is developed from an electrostatic latent image is not transferred to a medium such as paper.
Simultaneously satisfying the low-temperature fixing property and the high-temperature anti-offset property is a very difficult technical challenge. Numerous efforts have been made to address this technical challenge. A toner typically includes a colorant, a binder resin, and a releasing agent. For example, it is known that the low-temperature fixing property and the high-temperature anti-offset property may be simultaneously satisfied by using, as the binder resin of the toner, a mixture of a low molecular weight resin having a critical molecular weight or less and a high molecular weight resin having a very large molecular weight. With respect to this approach, the low molecular weight resin and the high molecular weight resin each independently control the low-temperature fixing property and the high-temperature anti-offset property, respectively. In the low molecular weight resin having a critical molecular weight or less, less entanglement between its molecular chains may occur. Accordingly, the low molecular weight resin having a critical molecular weight or less may reduce the MFT of the toner. In contrast, in the high molecular weight resin having a very large molecular weight, a lot of entanglement between its molecular chains may occur. Thus, the high molecular weight resin having a large molecular weight may allow the toner to maintain its elasticity even at a high temperature. That is, the high molecular weight resin having a very large molecular weight may improve the high-temperature anti-offset property of toner. The releasing agent (e.g., wax) may function to allow toner to be easily exfoliated from a developing roller. Accordingly, the releasing agent may also improve the anti-offset property of toner. It is known that it is preferable that the releasing agent (e.g., wax) has appropriate compatibility or miscibility with a binder resin. When the compatibility or miscibility of the releasing agent and the binder resin is excessively high, the amount of wax grains protruding from the surface of the toner may increase to cause the contamination of components, such as a developing roller, a photoreceptor, and a carrier. Also, in order for toner to be fully functional, it is preferable that the toner have image durability, flowability, and high-temperature preservability in addition to the low-temperature fixability and the high-temperature anti-offset property.
Thus, with respect to the conventional toner, the selection of appropriate physical properties of a binder resin and a releasing agent is focused on enabling the coexistence of low-temperature fixability, high-temperature anti-offset property, image durability, flowability, and high-temperature preservability.